It is well known in the art to mount electronic components to rigid and printed circuit boards. Typically, solder paste is applied to conductor pad regions on the rigid or substrate. Components are then placed with their terminals contacting the solder paste in the pad regions. The substrate is then exposed to relatively high temperatures to activate the solder paste which melts and then solidifies to bond and electrically connect the components onto the substrate.
A technique for mounting components onto flexible polyester substrates with low softening temperatures is taught by Annable in U.S. Pat. No. 5,898,992. The flexible substrate is fixed to a carrier support member. A cover is placed over the substrate. The cover has openings corresponding to component locations and with the carrier forms a carrier assembly. Solder paste is applied to the conductor regions of the substrate having component pads. Electronic components are then placed on the substrate with their terminals in contact with the solder paste. The carrier assembly is then pre-heated in a reflow oven to a temperature below the melting point of the solder paste. The assembly is then subjected to a rapid rise in temperature utilizing a supplemental heat source such as a heated gas jet. The cover shields the substrate from the high reflow temperatures and minimizes distortion of the flexible substrate during reflow.
While the prior art teaching achieves its intended purpose significant improvements are needed. For example, it would be desirable to eliminate the need for a special cover for shielding specific areas of the substrate from the heat generated by the gas jet. Additionally, a process for reflowing lead-free solder disposed between a substrate and a plurality of electronic components thereon is not addressed by the prior art and is therefore needed.